The blades were originally from the continent of akavir, home of the dragons. The continent Akavir launched 3 assaults in Tamriel these assaults were coordinated by the Tsaesci a snake like race of vampires in the region of Tsaesci. the blades were out at pale pass reman cyrodiil spoke with the blades general. This led to the blades becoming the emperor's personal guards. During the Oblivion crisis the blades were escorting Uriel Septim who was then murdered by the cultists of the Mythic Dawn followers of Mancar Cameron author of Commentaries on the mysterium xarses these eight books are present during oblivion and skyrim, however these books can only be found in silus vesius's house in dawnstar. Also during the oblivion crisis the blades guarded the emperor's last son martin septim. When the oblivion crisis ended the blades were disbanded, this happens before the great war. During the great war the blades were hunted down by the aldmeri dominions thalmor justiciaries, this leads to almost every last blades temple's destruction all except sky haven in sky rim and a few others which we never see but we do hear about them. That was just a brief history of the blades I forgot to mention that they hunted dragons before they met reman cyrodiil and everyone hates Delphine because she wants to kill paarthunax.